1. Field of the Invention
The present invention relates to a unitary hydroformed roof support pillar for a vehicle.
2. Background Art
Roof support pillars support the roof of a vehicle and are located between the windows and doors of a vehicle. Roof support pillars are frequently identified as A, B, C and in some instances D-pillars depending on the vehicle style. A B-pillar is generally located immediately behind the front door of a vehicle. The B-pillar is an important element in determining roof strength and the degree of side impact intrusion.
Passenger vehicle designs are tested for roof strength and side impact strength. Conventional B-pillars are fabricated as multiple stamped sheet metal parts that are generally spot welded together. It is possible to improve the strength of conventional B-pillars by forming the sheet metal parts from high grade material, such as dual phase and boron steels. B-pillars may also be made stronger by using thicker gauge sheet metal components. However, the use of high strength alloys and thicker sheet metal may increase the weight of a vehicle and also increases the cost to manufacture the B-pillar. Even with the use of thicker alloy components, B-pillars of conventional design may not always meet stringent test requirements for roof strength and side impact performance.
It has been proposed to use hydroformed tubes to fabricate vehicles having space frame construction in, for example, U.S. Pat. No. 6,282,790. This patent proposes integrally forming two B-pillars and a roof bow in a single U-shaped piece that is connected to the top surface of two tubular rockers. This proposed design presents a manufacturing problem in that the closed box section of the parts precludes spot welding assembly techniques. Also, the longitudinal thickness of the hydroformed tube portion between vehicle doors is objectionable from a styling standpoint.
Other proposed designs for hydroformed B-pillars are disclosed in published U.S. patent application US 2004/0239091 A1 and published U.S. patent application US 2005/0023865 A1. However, these proposed designs require reinforcing brackets to connect the B-pillar to a roof rail. In addition, the B-pillar is not reinforced by the roof rail and rocker panel members. In the event of a side impact intrusion, the connection of the B-pillar to the roof rail and rocker must rely upon welds for structural integrity. In addition, the width of the B-pillar in the longitudinal vehicle direction limits styling and adversely impacts vehicle appearance.
The present invention is directed to solving the above problems and other problems relating to the manufacture of a roof support pillar with minimum part count and improved roof crush and side impact performance. Prior art methods of hydroforming roof support pillars face technical barriers relating to the hydroforming procedure, methods of joining hydroformed components and packaging constraints. In particular, it is difficult for a hydroformed tube that has a uniform perimeter to accommodate desired section variations for vehicle styling.
Prior art multiple-piece B-pillars are designed to connect the roof rail, rocker and body outer panels. Connection between these elements are critical for vehicle body strength and noise, vibration and hardness (NVH) joint stiffness. Packaging constraints for B-pillars include providing clearance for seatbelt retractors and adequate mounting surfaces for door latch and hinge reinforcements.
The above problems and design challenges are addressed by applicants' invention as summarized below.